In conventional ink direct-storage type writing implements, a longitudinal groove which establishes the communication between annular storage grooves as the ink storage body and the ink chamber is bored directly from the storage grooves to the ink chamber through the flange so that the ink pushed out from the ink chamber is conducted through the longitudinal groove and stored in the storage grooves. This longitudinal groove also serves as an air replacing groove, admitting air into the ink chamber through itself within the flange when the pressure in the ink chamber reduces as ink is consumed.
With the conventional ink storage body incorporated in the barrel cylinder, the flange at the rear of the ink storage body closely fits the inner wall of the barrel cylinder so that no clearance will be formed on the outer peripheral surface of the flange except at the longitudinal groove. For this purpose, the variations in the inside diameter dimension of the barrel cylinder and the deformation of the shape thereof as well as the variations in the outside diameter dimension of the flange and the deformation of the shape thereof are taken into account. That is, the flange of the ink storage body is squeezed into the barrel cylinder so that the flange and the inner wall of the barrel cylinder change in shape to closely fit to one another absorbing the variations in the size and the deformation of the shapes. Thus, the flange and the inner wall of the barrel cylinder will not leave any gap therebetween.
In the above configuration, however, when the flange of the ink storage body is squeezed and fitted into the barrel cylinder, the storage body is inwardly stressed so that the flange changes in shape in such a way that the longitudinal groove becomes narrowed since the flange is slotted to half its radius because of the longitudinal groove. For this reason, the width of the longitudinal groove will not be constant because of the variations in the inner diameter dimension and deformation of the barrel cylinder and the variations in the outside diameter dimension and deformation of the flange.
The longitudinal groove has the function of conducting the ink pushed out from the ink chamber to the storage grooves for storing it, and the air replacing function of admitting air into the ink chamber through itself within the flange when the pressure in the ink chamber reduces as ink is consumed. Therefore, in the case where the width of the longitudinal groove is too narrow, if air in the ink chamber expands due to a temperature rise, etc., it disturbs the flow of the ink which should be pushed out from the ink chamber to the storage grooves, at the narrowed longitudinal groove in the flange, possibly causing accidental ink leakage from the writing point. Or, when the pressure in the ink chamber reduces with the consumption of ink, air must enter through the longitudinal groove in the flange, but the narrow width of the longitudinal groove makes it difficult for air to enter. In this case, the pressure in the ink chamber is hard to restore and remains low, causing a bad writing sensation with poor ink flow from the writing point, or causing ink starving during drawing lines.